[sksg] Refine invalidation logic

We need to discriminate between nodes whose bounds updates contribute to the dirty
region, and nodes whose bounds changes do not.

E.g. animated shape in a group: the animated shape node bounds should yield damage,
but the ancestor group bounds should not.

To accomplish this, we refine the invalidation state:

  1) self invalidation == the node itself was invalidated, and its bounds updates
     yield damage.
  2) descendant invalidation == the node has some (self-)invalidated descendant,
     but its own bounds are not contributing damage.

Also:

  * hoist the bounding box invalidation logic into the base class (Node::revalidate)
    and update to respect the states described above.
  * remove (now-redundant) GeometryNode bbox logic.
  * update revalidation methods to return the node bbox instead of void

TBR=
Change-Id: I8023d1793fb501c945a53f2dc2d2983e5b620ade
Reviewed-on: https://skia-review.googlesource.com/90581
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
diff --git a/experimental/sksg/SkSGDraw.h b/experimental/sksg/SkSGDraw.h
index f5146de..20ead3d 100644
--- a/experimental/sksg/SkSGDraw.h
+++ b/experimental/sksg/SkSGDraw.h
@@ -34,7 +34,7 @@
 
     void onRender(SkCanvas*) const override;
 
-    void onRevalidate(InvalidationController*, const SkMatrix&) override;
+    SkRect onRevalidate(InvalidationController*, const SkMatrix&) override;
 
 private:
     sk_sp<GeometryNode> fGeometry;